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Renewable Energy Essentials:Concentrating Solar Thermal Power

www.iea.org

OECD/IEA, 2009

n Concentrating solar thermal power (CSP) turns sunlight into electricity.

n CSP requires clear skies and strong sunlight, which is abundant in the southwestern United States, Mexico,North Africa, the Middle East, Central Asia, South Africa and Australia. Southern Europe and parts of Chinaand India may also have sufficient solar resources.

n Concentrated solar thermal power provides firm, peak, intermediate or base load capacities due to thermalstorage and/or fuel back-up.

n CSP technology showed especially strong growth in Spain and the United States since 2006. Installedcapacities near 1 gigawatt (GW) and projects under development or construction exceed 15 GW worldwide.

n Investment costs range from USD 4.2 to 8.4 per watt, depending on the solar resource and the size of thestorage. Levelised electricity costs range from US cents 17-25 per kWh, mostly depending on the quality ofthe solar resource.

n

Energy costs are expected to decrease as more suppliers enter the market and as a result of R&D efforts andlearning. In good sites, they could break the threshold of US cents 10 in fewer than ten years.

n The BLUE scenario of the IEA publication, Energy Technology Perspectives 2008, foresees that CSP willprovide 5% of world electricity by 2050. Preliminary results of the forthcoming IEA CSP Roadmap suggesta contribution of 12% to global electricity supply by 2050.

Market status Concentrated solar thermal power (CSP) is a re-emerging market. The Luz Company built 354 MWe of commercialplants in California, still in operations today, during 1984-1991. Activity re-started with the construction of an11-MW plant in Spain, and a 64-MW plant in Nevada, by 2006. There are currently hundreds of MW underconstruction, and thousands of MW under development worldwide. Spain and the United States togetherrepresent 90% of the market. Algeria, Egypt and Morocco are building integrated solar combined cycle plants,while Australia, China, India, Iran, Israel, Italy, Jordan, Mexico, South Africa and the United Arab Emirates are

finalising or considering projects.

While trough technology remains the dominant technology, several important innovations took place over2007-2009: the first commercial solar towers, the first commercial plants with multi-hour capacities, the firstLinear Fresnel Reflector plants went into line.

Concentrating sunrays requires clear skies, which are usually found in semi-arid, hot regions. The resourceis measured as Direct Normal Insolation (DNI), which is the energy received on a (tracking) surface

Figure 1: Direct Normal Insolation in kWh/m2.y and on-going projects

Breyer & Kniess 2009, after DLR-ISIS, plus IEA information.

Recent trends

The solarresource: DNI

3 000 kWh/m2/y

2 500 kWh/m2/y

2 000 kWh/m2/y

1 500 kWh/m2/y

1 000 kWh/m2/y

500 kWh/m2/y

0 kWh/m2/y

Legend: ; ; ; xx: capacity in MWe. +: indicates large storage capacities(the capacity of the power plant is larger than the electrical capacity indicated); xx/yy: for Integrated Solar Combined Cycle or fuel saver systems,xx indicatesthe solarcapacity, yy indicatesthe overall capacity.

existing capacities capacities under construction announced capacities

USA ;;

;;

troughs 424Fresnel 177troughs 1583towers 645dishes 800

Australiafuel saverFresnel 2/2000

IranISCC troughs 67/450

Emiratestroughs 100

Jordantroughs 100

Israeltroughs 100

Algeria,

;ISCC troughs20/470140/800

Spain ;;;

troughs 100+towers 31troughs 660+tower 17+ Egypt

ISCC troughs 25/150

South Africatower 100

MoroccoISCC troughs25/150

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perpendicular to the sunrays. Areas suitable to CSP technologies are found between 15 to 40 parallels and occasionally at higher latitude. The most favourable areas, shown in Figure 1, are found in large partsof North Africa, Middle East, southern Africa, western India, the southwestern United States, Mexico, placesin South America, and Australia. Other suitable areas are in the extreme south of Europe and Turkey, central

Asian countries, western China. Satellite data and regional climatic mapping must be confirmed with DNImonitoring on the ground.

The building of CSP plant creates eight to ten jobs per megawatt of equivalent electrical solar capacity in the

construction and manufacturing of components.

For large state-of-the-art trough plants, investment costs are in a range of USD 4.2 to 8.4 per Watt dependingon labour and land costs, technologies, the quality of the solar resource (DNI) and the sizes of storage andsolar field.

Levelised electricity costs range from USD 170 to 250 per MWh for large trough plants, depending mostly onthe solar resource (assumptions: 30 years economic lifetime, 8% discount rate).

When there is large storage capacity, the investment costs increase significantly with the size of the solar fieldbut so does the electrical output, so the energy cost changes only marginally. If storage serves to extend theproduction, energy costs will slightly decrease as smaller turbines can be used.

As cumulative capacities increase, investment costsand energy costs will decrease to an estimatedrange of USD 97 to 130 per MWh by 2015-2020,assuming learning rates of 12% for the solar-specificinvestments and of 5% for the power block andbalance of plant investments.

The deployment of CSP plants is driven by feed-intariffs in Spain, and Renewable Energy PortfolioStandards and a grant programme in the UnitedStates. Projects in Egypt and Morocco are supportedby grants from the Global Environment Facility.

Algeria, South Africa and the Gujarat State in Indiahave also established feed-in tariffs for CSP.

The Mediterranean Solar Plan of the Union for the Mediterranean is likely to initiate a wave of new projectson the south shore of the Mediterranean Sea. Of a total of 20 GW renewable energy capacities expected by2020, half or more might be CSP plants. Exports of renewable electricity to the European Union would providea strong incentive.

Low costs of fossil fuels remain an important barrier on grid even more so in countries where fossil fuelsprices are kept below world prices by direct or indirect government subsidies. Suitable areas are often semi-aridand water scarcity might be an issue, unless costlier dry cooling is used. Permitting and connection to the gridmight also be challenging.

The technical potential for CSP is virtually unlimited. An area of 100 miles squared in Nevada could powerthe entire US economy. The technical potential of the Middle East and North Africa (MENA) is more than onehundred times the total current electricity consumption of the MENA and European regions together. High

voltage direct current (HVDC) transport lines may allow CSP suitable areas to feed energy-demand centres.

In the Advanced Scenario of their publication CSP Global Outlook 2009, the IEA SolarPACES Programme,the European Solar Thermal Electricity Association and Greenpeace have estimated the global CSP capacity by2050 at 1500 GW. With large storage and solar fields, the yearly output would be 7 800 TWh, or 670 milliontonnes oil equivalent.

In a detailed study of renewable energy potential in the Middle-East North Africa Region, the GermanAerospace Center (DLR) has estimated that CSP plants could possibly provide by 2050 about half the regionselectrical production, from a total of 390 GW CSP capacities.

Technical potential

Economics

Long-termscenarios

OutlookGrowth drivers

Barriers

Figure 2: Levelised electricity cost from CSP plantsSource: IEA analysis. Assumption: 16 GW global

CSP capacity by 2015-2020.

Manufacturing

and employment

Investment costs

Generation costs

Cost reductions

Desert

clima

t

Sev

ille

Spa

in

2015 - 2020

2015 - 2020

0 50 100 150 200 250

Today

Today

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In the Blue Scenario of the IEA publication, EnergyTechnology Perspectives(ETP) 2008, where globalenergy-related CO

2 emissions are down to half

their 2005 level by 2050, CSP would globallyproduce 2 200 TWh at the time from a capacity of

630 GW. CSP would thus contribute to about 5%of global electricity production (see Figure 3).

Preliminary results of the forthcoming IEA CSP Roadmap suggest a solar contribution from CSP of 12% toglobal electricity supply by 2050.

In regions with suitable solar resources, peak electricity loads are increasingly driven by air-conditioningsystems; there is a good match between loads and resources. Further, CSP technologies are usually open toboth thermal storage and fuel back-up, offering systemic advantages.

Thermal storage and fuel back-up increase thevalue of the plant by providing guaranteedcapacities. Storage can be used to extend

the electricity generation after sunset, whenelectricity loads remain high. Storage could alsoserve round-the-clock, base-load generation,displacing, e.g.high-CO

2emitting coal plants.

Cheap back-up with some fuel can extend the guarantee of full capacity to winter periods avoiding costlyextra-investment in the solar field. This can be especially useful at a system level as other renewable energytechnologies (e.g.wind turbines) cannot offer guaranteed capacity.

Life-cycle CO2emissions of solar-only CSP plants are assessed at 17 g/kWh against, e.g., 776 g/kWh for coalplants and 396 g/kWh for natural gas combined cycle plants.1However, to the extent that some fossil fuel isused as a back-up, a CSP plant or an ISCC cannot be qualified as a zero-emitting plant. InEnergy TechnologyPerspectives 2008, CSP would save annually about 1 260 Mt CO

2in the BLUE scenario 7% of a total 18 Gt

CO2avoided in electricity production relative to the reference scenario. Other polluting emissions from SO

x

to NOx, metals and particulate matters would also be avoided.

An 80 MW trough plant requires about 1.2 million cubic meters of water per year, mostly for cooling thesteam cycle, and for cleaning the mirrors. Dry air cooling systems could considerably reduce the consumptionof water, at a cost.

The use of molten salts and synthetic oil in a CSP plant bears some risk of spillage or fire. This may in turn

hinder acceptance of a project by the local population.There are four main technologies, shown in Figure 5. Troughs and Fresnel reflectors track the sun on one axis,while dishes and towers track the sun on two axes.

Troughs or parabolic cylinders concentrate the solar rays on long heat collector pipes (moving with thetroughs). Current plants use some synthetic oil as heat transfer fluid. Alternative concepts include direct steamgeneration, and the use of molten salts as transfer fluid.

Troughs represent the most mature technology and the bulk of current projects; some have significant storagecapacities. Their solar to electricity conversion can reach than 15% (annual mean value).

Linear Fresnel reflectors(LFR) use slightly curved mirrors reflecting the solar rays on a long, fixed receiver.Investment costs per mirror area are lower but the annual efficiency remains below 10%. Saturated steam isdirectly generated in the receiver tubes.

1. External Costs from Emerging Electricity Generation Technologies, NEEDS, 2009.

Figure 3: Growth of global renewable electricity

production in the BLUE Scenario of ETP 2008

System-related

aspects

700

600

500

400

300

200

100

0 2005 2010 2020 2030 2040 20502015 2025 2035 2045

Blue

Act

GW

Environmentalimpacts

Life-cycle emissions

Solardirect

Fromstorage

Fossilbackup

MW

Time of day

50

40

30

20

10

00 2 4 6 8 10 12 14 16 18 20 22 24

Firm

capacity line

To storage

Figure 4: Round-the-clock operation of a CSP

plant with storage and back-up

Source: Geyer, SolarPACES Annual Report 2007

Local impacts

Technologystatus anddevelopment

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R&D priorities

Storage andintegration

Towers or central receiver systems (CRS), concentrate the sunrays on top of a fixed tower. This allows forhigher temperatures and efficiencies than linear systems. Towers can generate saturated or superheated steamdirectly, or use molten salts, air or other media as heat transfer fluids. Solar fields of thousands of smallheliostats are proposed as a cheap alternative to state-of-the-art field design.

Parabolic dishesconcentrate the sunrays on a focal point that is moving together with the dish tracking thesun, offering the highest optical efficiency on much smaller capacities (typically tens of kW). Mass productionmay allow them to compete with the larger systems, which benefit from economies of scale. Dish systems areless compatible with thermal storage than other CSP technologies, but require no cooling water.

Trough plants, linear Fresnel reflectors and most tower designs can be completed with heat storage and/orfuel back-up. The current reference technology for storage is based on molten salts.

Integrated Solar Combined Cycle power plants are relatively small solar fields in large combined cycle gas-fired plants. The heat from the solar field increases the production of the bottom steam cycle.

Research and development efforts so far, most of them taking place within the IEA Solar PACES ImplementAgreement, have been supported in particular by Germany, the European Commission and the US Departmentof Energy.

Improvements can be expected on all components of CSP plants. One possible step improvement with troughswould be direct steam generation, increasing the overall efficiency. Phase-change materials and concrete offernovel options for storage.

Towers have even greater room for improvements. Many innovative designs are currently proposed, withone or several towers sharing fields of heliostats, a great variety of central receiver designs, heat fluids andstorage options.

Towers with air receivers feeding the gas turbine of a combined cycle power plant could offer record solar-to-electricity efficiency of around 35%.

Other possible applications are industrial process heat and brine water desalination. The production of solarfuels such as hydrogen and other energy carriers can take several roads, notably in conjunction with fossil fuels

but reducing their carbon footprint (see Figure 6); it still requires significant R&D efforts.

Figure 5: Troughs, towers, LFR and dishes

Source: CSP Global Outlook 2009.

Linear Fresnel reflector (IFR) Central receiver Parabolic dish Parabolic trough

Curvedmirrors

Absorber tubeand reconcentrator

Central receiver

Heliostats

Receiver/engine

Reflector

Reflector

Absorber tube

Solar field piping

Concentrated solar energyWater splitting Decarbonisation

Water Fossil fuels (NG, oil, coal)

Solar electricity+ electrolysis

Optional COsequestration

2

Solar thermolysis Solar gasification

Long-term goal

Solar thermo-chemical cycle

Solar reforming

Short/mid-term

transitionSolar hydrogen

Figure 6: Different ways of producing hydrogen from solar energy

Source: Steinfeld, 2005.